/**
 * Copyright (c) 2011-2023, James Zhan 詹波 (jfinal@126.com).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.jfinal.template.expr.ast;

import java.util.ArrayList;
import java.util.List;
import com.jfinal.template.TemplateException;
import com.jfinal.template.stat.Scope;

/**
 * ExprList
 */
public class ExprList extends Expr {

    public static final Expr NULL_EXPR = NullExpr.me;
    public static final Expr[] NULL_EXPR_ARRAY = new Expr[0];
    public static final ExprList NULL_EXPR_LIST = new ExprList(new ArrayList<Expr>(0));

    public static final Object[] NULL_OBJECT_ARRAY =  new Object[0];

    private Expr[] exprArray;

    public ExprList(List<Expr> exprList) {
        if (exprList.size() > 0) {
            exprArray = exprList.toArray(new Expr[exprList.size()]);
        } else {
            exprArray = NULL_EXPR_ARRAY;
        }
    }

    /**
     * 持有 ExprList 的指令可以通过此方法提升 AST 执行性能
     * 1：当 exprArray.length == 1 时返回 exprArray[0]
     * 2：当 exprArray.length == 0 时返回 NullExpr
     * 3：其它情况返回 ExprList 自身
     *
     * 意义在于，当满足前面两个条件时，避免掉了 ExprList.eval(...) 方法中的判断与循环
     */
    public Expr getActualExpr() {
        if (exprArray.length == 1) {
            return exprArray[0];
        } else if (exprArray.length == 0) {
            return NULL_EXPR;
        } else {
            return this;
        }
    }

    public Expr[] getExprArray() {
        return exprArray;
    }

    public Expr getExpr(int index) {
        if (index < 0 || index >= exprArray.length) {
            throw new TemplateException("Index out of bounds: index = " + index + ", length = " + exprArray.length, location);
        }
        return exprArray[index];
    }

    public Expr getFirstExpr() {
        return exprArray.length > 0 ? exprArray[0] : null;
    }

    public Expr getLastExpr() {
        return exprArray.length > 0 ? exprArray[exprArray.length - 1] : null;
    }

    public int length() {
        return exprArray.length;
    }

    /**
     * 对所有表达式求值，只返回最后一个表达式的值
     */
    public Object eval(Scope scope) {
        // 优化：绝大多数情况下 length 等于 1
        if (exprArray.length == 1) {
            return exprArray[0].eval(scope);
        }

        if (exprArray.length == 0) {
            return null;
        }

        int end = exprArray.length - 1;
        for (int i=0; i<end; i++) {
            exprArray[i].eval(scope);
        }
        return exprArray[end].eval(scope);
    }

    /**
     * 对所有表达式求值，并返回所有表达式的值
     */
    public Object[] evalExprList(Scope scope) {
        if (exprArray.length == 0) {
            return NULL_OBJECT_ARRAY;
        }

        Object[] ret = new Object[exprArray.length];
        for (int i=0; i<exprArray.length; i++) {
            ret[i] = exprArray[i].eval(scope);
        }
        return ret;
    }
}




